A wave gear device comprises a rigid internally toothed gear, a flexible externally toothed gear disposed on the inside of the internally toothed gear, and a wave generator that bends the flexible externally toothed gear into an elliptical shape and causes the externally toothed gear to partially mesh with the rigid internally toothed gear. When the wave generator is rotated by a motor or the like, the positions where the two toothed gears are enmeshed with each other move in a circumferential direction, and relative rotation whose speed is reduced in accordance with the difference in the number of teeth between the toothed gears is generated between the two toothed gears. One of the gears is nonrotatably fixed to allow reduced-speed rotation to be output and transmitted to the load from the other toothed gear.
The wave generator comprises a rigid plug attached to a motor axle or the like, and a flexible bearing mounted on an elliptical external circumferential surface of the rigid plug. The flexible bearing has the same structure as a typical radial ball bearing, but the inner and outer races of the flexible bearing form a flexible bearing ring capable of bending in a radial direction. The flexible bearing is mounted between the elliptical external circumferential surface of the rigid plug and an internal circumferential surface of the flexible externally toothed gear. The flexible bearing holds the rigid plug and the flexible externally toothed gear in a state in which the plug and the gear can rotate relative to each other.
Wave gear devices can be divided into three types: flat type, cup type, and “silk hat” type, according to the shape of the flexible externally toothed gear. These types of wave gear device are disclosed in Patent Documents 1, 2, and 3.
[Patent Document 1] JP-A 05-172195
[Patent Document 2] JP-A 08-166052
[Patent Document 3] JP-U 02-91238
Wave gear devices have few components, highly precise rotary transmission, and a high reduction ratio; therefore, they are incorporated and used in drive mechanisms for robot arms and the like. In recent years, there has been a growing demand for higher-performance, higher-speed robots, and this has been accompanied by a growing demand for a higher performance, and particularly for an extended service life, in wave gear devices. In order to extend the service life of wave gear devices, it is essential to extend the service life of the flexible bearing in a wave generator in which the flexible externally toothed gear is rotationally moved while being bent.
However, up until the present time, no consideration has been given to extending the service life of flexible bearings in which the inner and outer races are rotated while being bent in the radial direction. Specifically, it bas been a few decades since the wave gear device has come into practical use, but the components constituting the flexible bearing have merely been used unmodified all this time without any changes being made to their dimensions.
An object of the present invention is to improve the flexible bearing that rotates while bending in a radial direction in a wave gear device, and to extend the service life of the bearing.